Air quality expert group - Fine particulate matter (PM2.5) in ... - Defra

PM2.5 in the UK
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with larger deviations in emissions from the original baseline scenario used to
derive the source–receptor relationships (that is the response of concentrations
at a receptor point to unit changes in emissions from a specified source).
31. As an alternative, some models such as PCM use an empirical approach to SIA
concentrations, interpolating between measurements; for example, see Figure
5.7 for PM2.5 maps of SO4 2- , NO3 - and NH4 + derived from the measurement
network in 2009 and scaled for the PM2.5 fractions. This approach is subject to
interannual variations in measurements influenced by different meteorology
in different years, and still leaves the problem of making forward projections.
By comparison, Figure 5.8 shows corresponding PM2.5 maps for the same
components calculated using the integrated assessment model UKIAM (A2.9).
This model utilises source–receptor relationships from a combination of models,
trying to best reflect the strengths of the EMEP model at the European scale and
the FRAME model at the UK scale. Comparison studies based on straight use
of the FRAME model result in population-weighted mean concentrations of SIA
around 20% lower than when using the EMEP model.